The present invention relates in general terms to brain research instrumentation. More particularly, the present invention provides brain research instrumentation including an array of implantable independently adjustable electrodes capable of, but not limited to, recording from freely moving animals. The invention may also be used for in vitro neurophysiological research wherein tissue slices are investigated. It may also be used to perform neurophysiological research on humans. Potential future uses of the invention include clinical diagnostic uses in both humans and animals.
Prior art brain research instrumentation includes movable single channel or single electrode mechanisms which were limited to recording from single locations in the brain. Early research tended to be concentrated in sensory portions of the brain such as the visual cortex. For example, the research would seek to identify what particular stimulus in the subject's visual field would cause an individual neuron in the visual cortex to fire. The prior art single electrode mechanisms were capable of being moved to different locations in the brain but were only capable of recording from a single neuron or a small neuron cluster at a time.
The prior art also includes apparatus with multiple electrodes whose position in space is fixed relative to the other electrodes. These prior art electrodes are capable of recording timing or firing patterns of multiple neurons or multiple small clusters of neurons. The importance of being able to record timing patterns is critical to understanding higher order functions of the brain. However, the multi-channel or multi-electrode prior art devices could only be used in restrained animal subjects and were not capable of being moved within the brain. Thus, the timing patterns that could be recorded within the brain were limited by the number of electrodes and to only those patterns that occurred between the individual neurons or small neuron clusters that happen to be near the tips of the recording electrodes. Another disadvantage of the fixed array of electrodes is that the research is inherently limited to those brain functions performed by a non-moving subject.
The present invention provides four significant improvements over the prior art. First, the present invention provides an increased number of recording electrodes, capable of recording a much larger combination of timing patterns. Secondly, the present invention provides electrodes which are independently adjustable, further increasing the number of recordable timing patterns by improving the "yield" or effectiveness of each electrode, as well as increasing the combinations of regions within the brain that may be examined in a given experiment. Thirdly, the present invention is small enough and lightweight enough to be easily carried on the skull of the subject animal and this allows for study of activities which involve free motion of the subject, for example, navigational skills and spatial orientation skills. The invention is not limited to use on freely moving subjects; it may be used on unconscious or restrained subjects, and may be used on in vitro tissue samples to study virtually any human or animal brain function. Fourth, the present invention enables the use of much fewer laboratory animals to gather the same amount of research data.
The increased number of electrodes vastly enlarges the capacity of the instrument to record timing patterns. For example, to measure timing patterns of the firing of two neurons, two single electrodes are necessary. As the number of recording electrodes increases, their capacity for recording timing patterns (i.e. sequential firing patterns of neurons) increases dramatically. In fact, if we assume that each electrode is recording effectively and recording independently of other electrodes in the array, it is believed that the increase in the number of timing patterns recordable increases with the factorial of the number of electrodes. For example, in the embodiment of the present invention with 48 separate recording electrodes, the number of timing patterns recordable (assuming each electrode records one neuron) would be 48 factorial (48|). To illustrate the theoretical capacity of the present invention, 48 factorial (48|) is approximately 1.24.times.10.sup.61 possible recordable and distinct firing patterns, whereas a prior art device with 20 stationary electrodes has a theoretical capacity of recording 20 factorial (20|) or approximately 2.43.times.10.sup.18 distinct, recordable firing patterns. The present invention has a capacity approximately 5.1.times.10.sup.42 times greater than the prior art, a gigantic step forward in trying to unravel the mystery of higher order brain functions.
A related advantage of a larger number of electrodes is the pairwise interaction, which increases as n.sup.2 where n is the number of electrodes.
Another advantage of the present invention is that, by independently moving the electrodes, we are capable of locating the recording tips at points of interest and increasing the "yield" of each electrode. By properly locating the electrodes, we can obtain a yield of useful recording from as many as 150 neurons with 48 electrodes. This can be accomplished by properly locating electrodes and identifying firing patterns of neurons between electrodes. In contrast, the prior art device using 20 non-movable electrodes typically has a yield of 10 to 15 neurons because the recording tips are not movable relative to each other and the array of 20 electrodes is not movable within the brain. The increased yield obtained by the present invention further increases the capacity of recording timing patterns.
It is believed that the present invention may in the future lead to an understanding of the learning process, diagnosis of learning disorders, possible spinal damage bypass (or "neural prosthesis") development, and various clinical diagnostic possibilities for both animals and humans.
Accordingly, a primary object of the present invention is to provide an implantable adjustable multi-electrode microdrive array capable of recording vastly more timing patterns of neural firing than recordable by devices of the prior art.
A further object of the invention is to provide a brain research instrument having an array of electrodes wherein the recording electrodes are independently adjustable.
Another object of the invention is to provide a neurophysiological research instrument with a yield greater than one, i.e., n electrodes are capable of recording as many as 3n neurons.
A further object of the invention is to provide a device for neurological research in animal subjects in which a much smaller number of subjects is needed in order to generate the same research data as would be required by using prior art devices.
A further object of the invention is to provide a device for neurophysiological research in conscious animal subjects wherein the animal subjects may move about freely.
A further object of the invention is to provide a device for neurophysiological research capable of investigating navigational and motion related brain activities, and related learning processes, which simply cannot be investigated in a restrained or unconscious subject.
Other objects and advantages of the invention will become apparent from the following description and the drawings wherein: